System and method for performing an engine stop and start for a rolling vehicle

ABSTRACT

Methods and systems for improving operation of a vehicle driveline that includes an engine and an automatic transmission with a torque converter are presented. In one non-limiting example, the engine may be stopped while a vehicle in which the engine operates is rolling. A transmission coupled to the engine may be shifted as the vehicle rolls so that vehicle response may be improved if a driver requests an increase of engine torque.

BACKGROUND/SUMMARY

An engine of a vehicle may be stopped and started during a vehicle drivecycle to conserve fuel. The engine may be stopped when the vehicle isstopped when driver demand torque is low. The engine may also be stoppedwhile the vehicle is moving during low driver demand torque conditionswhile an electric machine provides torque to propel the vehicle. Thestopped engine may be restarted if driver demand torque increases or ifa battery is to be charged. However, for vehicles that are not propelledvia an electric motor and that include an automatic transmission, it maybe difficult to stop the engine in response to low driver demand torquesbecause stopping the engine stops operation of a mechanically drivenpump in the transmission that supplies pressurized fluid to activatetransmission gears. Thus, the transmission may not operate as desired ifthe engine is stopped. Therefore, it may be desirable to provide a wayto stop an engine and maintain transmission operation during low driverdemand conditions so that engine fuel consumption may be reduced duringlow driver demand torque conditions and while the vehicle is stopped.

The inventors herein have recognized the above-mentioned issues and havedeveloped a method for operating a vehicle driveline, comprising:activating an electric transmission pump in response to a request tostop an engine; and adjusting a speed of the electric transmission pumpin response to a pressure in an accumulator.

By adjusting a speed of the electric transmission pump in response to apressure in the accumulator, it may be possible to provide the technicalresult of reducing energy consumption of a vehicle while shifting atransmission of the vehicle. In particular, the transmission may beshifted while the engine is stopped so that if a driver requests enginetorque, the transmission may be engaged in an appropriate gear for thepresent vehicle speed in a short period of time. In this way, thevehicle may respond quickly to a driver request even when an engine isstopped to improve vehicle drivability. Further, transmission electricpump speed may be adjusted responsive to an estimate of time betweengear shifts so that a desired pressure may be available to stroke a gearclutch in time for a next gear shift.

The present description may provide several advantages. For example, theapproach may reduce vehicle fuel consumption and improve response to adriver requesting driveline torque when an engine in the driveline isstopped rotating. Further, the approach may provide for partiallyengaging a plurality of gear clutches when an engine coupled to atransmission is stopped so that the transmission may be engaged in anappropriate gear for applying engine torque to vehicle wheels even asvehicle speed changes while the engine is stopped. Further still, theapproach may reduce electrical power consumption by adjusting a speed ofthe electrical transmission pump to a speed that meets but does notsignificantly exceed a speed to timely stroke one or more transmissionclutches during gear shifting. Additionally, the approach may providedesired shifting even when the transmission electric pump lacks flowcapacity to close a transmission clutch in a desired amount of time.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of an engine;

FIG. 2 shows a schematic depiction of an example vehicle drivelineincluding an engine;

FIG. 3 shows an example schematic for supplying transmission fluid totransmission clutches;

FIG. 4 shows an example clutch filling sequence and electrical pumpspeed during the clutch filling sequence;

FIG. 5 shows an example driveline operating sequence according to themethod of FIG. 6; and

FIG. 6 shows a flowchart of an example method for operating thedriveline.

DETAILED DESCRIPTION

The present description is related to operating a vehicle driveline thatincludes an engine that is directly coupled to a torque converter.Further, the torque converter is directly coupled to an automatictransmission. The engine may be configured as is shown in FIG. 1. Theengine of FIG. 1 may be incorporated into a vehicle driveline as shownin FIG. 2, and the engine may be the only adjustable torque source inthe driveline as is shown in FIG. 2. Transmission fluid may be directedto transmission clutches in a system as shown in FIG. 3. Pressurizedtransmission fluid may be supplied to one or more transmission clutchesas is shown in the sequence shown in FIG. 4. The driveline may operateas shown in FIG. 5 according to the method shown in FIG. 6.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Flywheel 97 and ring gear 99 arecoupled to crankshaft 40. Starter 96 (e.g., low voltage (operated withless than 30 volts) electric machine) includes pinion shaft 98 andpinion gear 95. Pinion shaft 98 may selectively advance pinion gear 95to engage ring gear 99. Starter 96 may be directly mounted to the frontof the engine or the rear of the engine. In some examples, starter 96may selectively supply torque to crankshaft 40 via a belt or chain. Inone example, starter 96 is in a base state when not engaged to theengine crankshaft. Combustion chamber 30 is shown communicating withintake manifold 44 and exhaust manifold 48 via respective intake valve52 and exhaust valve 54. Each intake and exhaust valve may be operatedby an intake cam 51 and an exhaust cam 53. The position of intake cam 51may be determined by intake cam sensor 55. The position of exhaust cam53 may be determined by exhaust cam sensor 57. Intake valve 52 may beselectively activated and deactivated by valve activation device 59.Exhaust valve 54 may be selectively activated and deactivated by valveactivation device 58.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Fuel injector 66 delivers liquid fuel in proportion to thepulse width from controller 12. Fuel is delivered to fuel injector 66 bya fuel system (not shown) including a fuel tank, fuel pump, and fuelrail (not shown). In one example, a high pressure, dual stage, fuelsystem may be used to generate higher fuel pressures.

In addition, intake manifold 44 is shown communicating with turbochargercompressor 162 and engine air intake 42. In other examples, compressor162 may be a supercharger compressor. Shaft 161 mechanically couplesturbocharger turbine 164 to turbocharger compressor 162. Optionalelectronic throttle 62 (e.g., central or engine intake manifoldthrottle) adjusts a position of throttle plate 64 to control air flowfrom compressor 162 to intake manifold 44. Pressure in boost chamber 45may be referred to as throttle inlet pressure since the inlet ofthrottle 62 is within boost chamber 45. The throttle outlet is in intakemanifold 44. In some examples, throttle 62 and throttle plate 64 may bepositioned between intake valve 52 and intake manifold 44 such thatthrottle 62 is a port throttle. Compressor recirculation valve 47 may beselectively adjusted to a plurality of positions between fully open andfully closed. Waste gate 163 may be adjusted via controller 12 to allowexhaust gases to selectively bypass turbine 164 to control the speed ofcompressor 162.

Air filter 43 cleans air entering engine air intake 42 via inlet 3 whichis exposed to ambient temperature and pressure. Converted combustionbyproducts are exhausted at outlet 5, which is exposed to ambienttemperature and pressure. Thus, piston 36 and combustion chamber 30 mayoperate as a pump when engine 10 rotates to draw air from inlet 3 andexhaust combustion byproducts to outlet 5. Inlet 3 is upstream of outlet5 according to a direction of flow through engine 10, exhaust manifold48, and engine air intake 42. Upstream does not include anything outsidethe engine past the inlet 3, and downstream does not include anythingoutside the engine past the outlet 5.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106 (e.g., non-transitory memory), random access memory 108, keepalive memory 110, and a conventional data bus. Controller 12 is shownreceiving various signals from sensors coupled to engine 10, in additionto those signals previously discussed, including: engine coolanttemperature (ECT) from temperature sensor 112 coupled to cooling sleeve114; a position sensor 134 coupled to an accelerator pedal 130 forsensing force applied by foot 132; a position sensor 154 coupled tobrake pedal 150 for sensing force applied by foot 152, a measurement ofengine manifold pressure (MAP) from pressure sensor 123 coupled tointake manifold 44; a measurement of engine boost pressure or throttleinlet pressure from pressure sensor 122; an engine position from a Halleffect sensor 118 sensing crankshaft 40 position; a measurement of airmass entering the engine from sensor 120; and a measurement of throttleposition from sensor 68. Barometric pressure may also be sensed (sensornot shown) for processing by controller 12. In a preferred aspect of thepresent description, engine position sensor 118 produces a predeterminednumber of equally spaced pulses every revolution of the crankshaft fromwhich engine speed (RPM) can be determined.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g., whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC).

During the compression stroke, intake valve 52 and exhaust valve 54 areclosed. Piston 36 moves toward the cylinder head so as to compress theair within combustion chamber 30. The point at which piston 36 is at theend of its stroke and closest to the cylinder head (e.g., whencombustion chamber 30 is at its smallest volume) is typically referredto by those of skill in the art as top dead center (TDC). In a processhereinafter referred to as injection, fuel is introduced into thecombustion chamber. In a process hereinafter referred to as ignition,the injected fuel is ignited by known ignition means such as spark plug92, resulting in combustion.

During the expansion stroke, the expanding gases push piston 36 back toBDC. Crankshaft 40 converts piston movement into a rotational torque ofthe rotary shaft. Finally, during the exhaust stroke, the exhaust valve54 opens to release the combusted air-fuel mixture to exhaust manifold48 and the piston returns to TDC. Note that the above is shown merely asan example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

Referring now to FIG. 2, FIG. 2 is a block diagram of a vehicle 225including a driveline 200. The driveline of FIG. 2 includes engine 10shown in FIG. 1. Engine 10 includes one or more torque actuators 204(e.g., a throttle, camshaft, fuel injector, etc.) Driveline 200 may bepowered by engine 10. Engine crankshaft 40 is shown coupled to dampener280, and dampener 280 is shown coupled to impeller 285 of torqueconverter 206. Torque converter impeller 285 is mechanically coupled totransmission pump 289. Transmission mechanically driven pump 289supplies pressurized transmission fluid to transmission clutches 210 and211. Torque converter 206 also includes a turbine 286 coupled totransmission input shaft 270. Transmission input shaft 270 mechanicallycouples torque converter 206 to automatic transmission 208 and its speedis monitored via speed sensor 217. Torque converter 206 also includes atorque converter bypass lock-up clutch 212 (TCC). Torque is directlytransferred from impeller 285 to turbine 286 when TCC is locked. TCC iselectrically operated by controller 12. Alternatively, TCC may behydraulically locked. In one example, the torque converter may bereferred to as a component of the transmission.

When torque converter lock-up clutch 212 is fully disengaged, torqueconverter 206 transmits engine torque to automatic transmission 208 viafluid transfer between the torque converter turbine 286 and torqueconverter impeller 285, thereby enabling torque multiplication. Incontrast, when torque converter lock-up clutch 212 is fully engaged, theengine output torque is directly transferred via the torque converterclutch to an input shaft 270 of transmission 208. Alternatively, thetorque converter lock-up clutch 212 may be partially engaged, therebyenabling the amount of torque directly relayed to the transmission to beadjusted. The controller 12 may be configured to adjust the amount oftorque transmitted by torque converter 212 by adjusting the torqueconverter lock-up clutch in response to various engine operatingconditions, or based on a driver-based engine operation request.

Automatic transmission 208 includes gear clutches 211 and forward clutch210 to engage or disengage gears 209 (e.g., reverse and gears 1-10). Thegear clutches 211 (e.g., 1-10) and the forward clutch 210 may beselectively engaged to propel a vehicle. Transmission 208 also includesan electrically driven pump 281 for supplying pressurized transmissionfluid to gear clutches 211 when engine 10 is not rotating. Transmission208 is configured such that one gear of gears 209 may be engaged byapplying two or more of clutches 211. In other words, a gear may bepositively engaged when two or more of clutches 211 are closed. Further,transmission 208 may enter a neutral state where input shaft 270 is notengaged with output shaft 260 when one or more of clutches 211 is openbut while one or more of clutches 211 are closed. For example,transmission 208 may be engaged in second gear when only first, third,and fourth clutches are engaged. Transmission may be in neutral whenonly first and third clutches are engaged. Torque output from theautomatic transmission 208 may in turn be relayed to wheels 216 topropel the vehicle via output shaft 260. Speed of output shaft 260 ismonitored via speed sensor 219. Specifically, automatic transmission 208may transfer an input driving torque at the input shaft 270 responsiveto a vehicle traveling condition before transmitting an output drivingtorque to the wheels 216.

Further, a frictional force may be applied to wheels 216 by engagingwheel brakes 218. In one example, wheel brakes 218 may be engaged inresponse to the driver pressing his foot on a brake pedal as shown inFIG. 1. In other examples, controller 12 or a controller linked tocontroller 12 may apply engage wheel brakes. In the same way, africtional force may be reduced to wheels 216 by disengaging wheelbrakes 218 in response to the driver releasing his foot from a brakepedal. Further, vehicle brakes may apply a frictional force to wheels216 via controller 12 as part of an automated engine stopping procedure.

Thus, in this example, engine 10 is the only adjustable torque sourcethat may provide torque to driveline 200. Torque flows from engine 10 totransmission 208 before being applied to wheels 216. Thus, engine 10 isupstream of torque converter 206, transmission 208, and wheels 216 in adirection of torque flow. Further, the system includes only three speedsensors including one at the engine crankshaft, one at the transmissioninput shaft, and one at the transmission output shaft.

Controller 12 may be configured to receive inputs from engine 10, asshown in more detail in FIG. 1, and accordingly control a torque outputof the engine and/or operation of the torque converter, transmission,clutches, and/or brakes. Further, controller 12 may receive driver inputfrom man/machine interface 299. As one example, an engine torque outputmay be controlled by adjusting a combination of spark timing, fuel pulsewidth, fuel pulse timing, and/or air charge, by controlling throttleopening and/or valve timing, valve lift and boost for turbo- orsuper-charged engines. In the case of a diesel engine, controller 12 maycontrol the engine torque output by controlling a combination of fuelpulse width, fuel pulse timing, and air charge. In all cases, enginecontrol may be performed on a cylinder-by-cylinder basis to control theengine torque output.

When rolling-stop conditions are satisfied, controller 12 may initiateengine shutdown to stop engine rotation by shutting off fuel and/orspark to the engine. When engine restart conditions are satisfied,and/or a vehicle operator wants to increase torque to vehicle wheels,controller 12 may reactivate engine 10 by cranking engine 10 andresuming cylinder combustion.

Referring now to FIG. 3, an example schematic for supplying transmissionfluid to transmission clutches is shown. Transmission system 300includes controller 12 and transmission 208. In this example, torqueconverter 206 is shown as part of automatic transmission 208, but insome examples it may also be considered as being separate from automatictransmission 208. Electrical connections are shown via dashed lineswhile devices and hydraulic connections or conduits are shown via solidlines.

Automatic transmission 208 includes a sump 370 that holds transmissionfluid 302. Electrically driven pump 281 and/or mechanically driven pump289 may supply transmission fluid 302 to transmission gear clutches 211.Electrically driven pump 281 is rotated via electric motor 303.Transmission fluid 302 may flow out of output 304 of electrically drivenpump 281 in the direction of the arrow on electrically driven pump 281.Transmission fluid may flow from electrically driven pump 281 to linepressure solenoid valve 308 by flowing through check valve 305. However,check valve 305 prevents transmission fluid from flowing intoelectrically driven pump 281. Line pressure solenoid valve 308 controlstransmission fluid pressure in passage or conduit 330. Excesstransmission fluid flow may be directed from line pressure solenoidvalve 308 back to sump 370 via passage or conduit 355. Transmissionfluid 302 may flow out of output 307 of mechanically driven pump 289 inthe direction of the arrow on mechanically driven pump 289. Transmissionfluid may flow from mechanically driven pump 281 to line pressuresolenoid valve 308 by flowing through check valve 306. However, checkvalve 306 prevents transmission fluid from flowing into mechanicallydriven pump 289.

In this non-limiting example, transmission 208 includes six clutchpressure control valves 310 that may direct transmission fluid 302 tosix gear clutches 211. The six pressure control valves 310 may beoperated individually, and more than one pressure control valve 310 maybe operated at a same time. For example, a sole gear of transmission 208may be engaged to couple an input shaft of automatic transmission 208 toan output shaft of automatic transmission 208 via closing a plurality ofgear clutches (e.g., clutches 1, 2, and 4). In this example, a firstgear clutch is the clutch closest to the top of FIG. 3. The second gearclutch is the second clutch closest to the top of FIG. 3, and so on. Ifone of the plurality of gear clutches (e.g., 1, 2, and 4) is notengaged, automatic transmission 208 is in neutral and the particulargear is partially engaged. Thus, a gear of automatic transmission 208may be partially engaged by fully closing a plurality of gear clutchesabsent fully closing one clutch of a total actual number of clutchesneeded to fully engage the selected transmission gear. Clutch pressurecontrol valves 310 adjust pressure of transmission fluid 302 in gearclutches 211 so as to increase or decrease a torque transfer capacity ofeach individual gear clutch 211. Transmission fluid 302 may be returnedto sump 370 via passage 354 when pressure in one or more of clutches 211is reduced to disengage a transmission gear.

Automatic transmission 208 also includes an accumulator 320 and anaccumulator flow control valve 312 positioned on an outlet side 321 ofaccumulator 320 to control flow of transmission fluid 302 into and outof accumulator 320. Pressure within accumulator 320 is sensed viapressure sensor 350. When mechanically driven pump 289 is rotating,pressurized transmission fluid may be stored in accumulator 320.Similarly, when electrically driven pump 281 is rotating and flow toclutches 211 is low, pressurized transmission fluid may be stored inaccumulator 320. However, if mechanically driven pump 289 is notrotating and electrically driven pump is active, valve 312 may be openedto assist electrically driven pump when flow to transmission clutches211 is at a higher level where a desired pressure downstream of linepressure solenoid 308 cannot be maintained by electrically driven pump281. Such a condition may be present during filling of one or more gearclutches 211. Thus, stored pressure in accumulator 320 may beselectively released to gear clutches 211 when electrically driven pumpflow does not or cannot maintain a desired pressure downstream of linepressure solenoid valve 308. Since transmission fluid flow originatesfrom sump 370 and proceeds to electrically driven pump 281 ormechanically driven pump 289 before reaching line pressure solenoidvalve 308, line pressure solenoid valve 308 is downstream ofelectrically driven pump 281 and mechanically driven pump 289.

Thus, the system of FIGS. 1-3 provides for a vehicle system, comprising:an engine; a transmission coupled to the engine and including a torqueconverter having a torque converter clutch, an electric pump, amechanical pump, an accumulator positioned downstream of the electricpump and the mechanical pump, and a valve positioned at an outlet sideof the accumulator; a controller including executable instructionsstored in a non-transitory memory for selectively stroking atransmission gear clutch without fully closing the transmission gearclutch in response to a request to improve vehicle drivability atexpense of vehicle energy consumption, and to not stroke thetransmission gear clutch in response to a request to improve vehicleenergy consumption at expense of vehicle drivability, the transmissionclutch stroked or not stroked while the engine is stopped. The vehiclesystem further comprises additional instructions for adjusting a speedof the electric pump in response to an estimate of an amount of timebetween transmission gear shifts. The vehicle system further comprisesadditional instructions for adjusting a speed of the electric pump inresponse to a pressure in the accumulator.

In some examples, the system further comprises additional instructionsfor stopping rotation of the engine in response to a driver demandtorque. The vehicle system further comprises additional instructions toshift the transmission to neutral in response to the driver demandtorque. The vehicle system further comprises additional instructions toactivate the electric pump in response to the driver demand torque.

Referring now to FIG. 4, an example clutch filling sequence is shown.The two prophetic plots are time aligned and occur at the same time. Thefirst plot from the top of FIG. 4 is a plot of clutch pressure versustime. The vertical axis represents clutch pressure and the horizontalaxis represents time. Clutch pressure increases in the direction of thevertical axis arrow. Time increases from the left to the right side ofthe plot.

The second plot from the top of FIG. 4 is a plot of electric pump speedversus time. The vertical axis represents electric pump speed andelectric pump speed increases in the direction of the vertical axisarrow. The horizontal axis represents time and time increases from theleft side of the plot to the right side of the plot.

At time T0, the electric pump speed is zero and the clutch pressure islow. The clutch is not being activated or applied. In other words, theclutch is open and not transferring torque. The engine coupled to thetransmission is not rotating (not shown) and the mechanical pump (notshown) within the torque converter is not rotating.

At time T1, the clutch pressure is increased and the electric pump speedis increased to stroke the clutch. The clutch is stroked when pressureis applied to the clutch plates to remove compliance between the clutchhousing and the clutch plates. However, the clutch transfers less than athreshold amount of torque when stroked, the threshold amount of torqueless than 5% of the clutches torque transfer capacity. Torque is notpurposefully transferred across the clutch between time T1 and time T2.

The electric pump speed may be increased in response to a request toclose the clutch or shift the transmission. The clutch pressure isincreased in response to a request to shift the transmission or closethe clutch. The transmission may be shifted in response to an increasein torque requested by a driver or in response to a driver releasing abrake pedal to indicate a change of mind condition of the driver.Further, the engine coupled to the transmission may be cranked andbegins to be started at time T1 (not shown).

If an accumulator 320 is included in the system, the accumulator flowcontrol valve 312 may be opened at time T1 to assist the electric pump.The electric pump speed may be adjusted to a first level indicated bysolid line 420 when an accumulator is present and the accumulator flowcontrol valve is opened. The electric pump speed may be adjusted to asecond level indicated by solid line 422 when an accumulator is notpresent and the accumulator flow control valve is not opened. Thus, theelectric pump speed may be increased to a higher level when the clutchis stroked without an accumulator present as compared to a speed theelectric pump is adjusted to if the accumulator is present. By operatingthe electric pump at a lower speed, electrical energy may be conserved.By operating the electric pump at a higher speed when the accumulator isnot present, the clutch may be filled in a shorter amount of time.

At time T2, the clutch pressure is increase a second time so as to beginpurposefully transferring torque across the clutch. The clutch pressureis boosted to provide more uniform clutch closing. Additionally, theelectric pump speed is increased as shown at 422 for no accumulatorpresent and at 420 for the accumulator being present to increase flow oftransmission fluid to the clutch to increase pressure applied to theclutch.

At time T3, the engine speed reaches a threshold speed (not shown) asthe engine is started and engine speed increases to match transmissionoutput shaft speed. Therefore, the electric pump is deactivated. In oneexample, the threshold speed is a speed at which the engine turns themechanical pump to provide a threshold amount of transmission fluid flowthrough the mechanical pump. The electric pump may be deactivated atthis time to conserve electrical energy because the mechanical pump hascapacity to close the transmission clutch in a desired amount of time.Additionally, the accumulator flow control valve 312 may be closed toreduce the possibility of transmission fluid flowing into theaccumulator when the clutch is being closed.

Between time T3 and time T4, the clutch pressure is reduced and thenincreased to continue to increase the clutches torque transfer capacity.The electrical pump remains deactivated.

At time T4, a speed difference across the clutch (not shown) issubstantially zero (e.g., less than 50 RPM). Therefore, clutch pressureis increased to fully close the clutch. The electric pump remainsdeactivated since the engine rotates at a speed where the mechanicalpump has capacity to close transmission clutches in a desired amount oftime. Further, the accumulator flow control valve may be opened aftertime T4 so that pressure in the accumulator may be recharged by themechanical pump without affecting the closing of the clutch.

In this way, electric pump speed and accumulator flow valve position maybe adjusted to close a gear clutch faster. Further, once the mechanicalpump speed is greater than a threshold speed, the accumulator flow valvemay be closed to decrease an amount of time it takes to close theclutch.

Referring now to FIG. 5, an example vehicle driveline operating sequenceis shown. The signals and sequences of FIG. 5 may be provided by thesystem shown in FIGS. 1-3 executing the method of FIG. 6. Verticalmarkers T10-T15 represent times of interest in the sequence. In thisexample, two engine stopping events are shown. The first engine stoppingevent occurs between times T11 and T13. It represents an engine stoppingevent where the engine is not restarted until after the vehicle isstopped. The second engine stopping event occurs between times T14 andT15. It represents an engine stopping event where the engine isrestarted before the vehicle comes to a stop.

The first plot from the top of FIG. 5 is a plot representing rollingstart/stop (RSS) status versus time. The horizontal axis represents timeand time increases from the left side of the plot to the right side ofthe plot. The vertical axis represents RSS status and RSS is active whenthe trace is at a higher level near the vertical axis arrow. RSS is notactive when the trace is at a lower level near the horizontal axis. RSSmay be activated to stop the engine and conserve fuel in response to alow driver demand torque or other conditions.

The second plot from the top of FIG. 5 represents vehicle speed versustime. The vertical axis represents vehicle speed and vehicle speedincreases in the direction of the vertical axis arrow. Vehicle speed iszero at the horizontal axis. The horizontal axis represents time andtime increases from the left side of the plot to the right side of theplot.

The third plot from the top of FIG. 5 represents engine speed versustime. The vertical axis represents engine speed and engine speedincreases in the direction of the vertical axis arrow. The horizontalaxis represents time and time increases from the left to the right sideof the figure.

The fourth plot from the top of FIG. 5 represents an engaged orpartially engaged transmission gear versus time. The vertical axisrepresents engaged or partially engaged transmission gear. The engagedor partially engaged transmission gear is indicated along the verticalaxis. The horizontal axis represents time and time increases from theleft to the right side of the figure. A partially engaged gear is a gearthat is activated by a plurality of clutches and one of the plurality ofclutch is not fully closed but the other clutches are fully closed.

The fifth plot from the top of FIG. 5 represents transmission electricpump speed versus time. The vertical axis represents transmissionelectric pump speed and electric pump speed increases in the directionof the vertical axis arrow. The horizontal axis represents time and timeincreases from the left to the right side of the figure.

The sixth plot from the top of FIG. 5 represents transmissionaccumulator pressure versus time. The vertical axis representstransmission accumulator pressure and accumulator pressure increases inthe direction of the vertical axis arrow. The horizontal axis representstime and time increases from the left to the right side of the figure.

At time T10, the RSS status is not asserted. Consequently, the engine isoperating and rotating. The vehicle speed is at a higher level and theengine speed is at a higher level. The transmission is engaged in 5^(th)gear and the transmission electric pump is off. The accumulator pressureis at a higher level.

At time T11, the RSS status transitions to active. Therefore, the engineis stopped rotating and the vehicle speed begins to decrease. The RSSmode may be activated in response to a driver releasing or partiallyreleasing an accelerator pedal (not shown). One of a plurality oftransmission clutches to engage 5^(th) gear is released so that 5^(th)gear is partially engaged. By releasing the one clutch, the transmissioninput shaft is decoupled from the transmission output shaft so thatengine speed may be reduced to zero while the vehicle wheels continue torotate. In other words, the transmission is in neutral with 5^(th) gearpartially engaged. The transmission's electric pump is activated shortlythereafter to maintain transmission line pressure. The transmissionelectric pump speed may be adjusted to a lower speed that allows thetransmission electric pump to maintain transmission line pressure whentransmission gear shifting is not present. The accumulator pressureremains at a higher level and the accumulator flow control valve (notshown) is closed.

At time T12, the transmission is downshifted from a partially engaged5^(th) gear to a partially engaged 4^(th) gear. The transmission may bedownshifted in response to a decrease in vehicle speed and transmissionshifting following a shift schedule. The transmission shift schedule maybe stored in memory and the table outputs a desired gear for a desiredvehicle speed and driver demand torque. The RSS remains active.Therefore, the engine remains stopped. The transmission electric pumpspeed is increased in response to the request to shift gears so that thegear clutches may close in a desired amount of time. Further, theaccumulator flow control valve (not shown) is opened in response to therequest to shift gears. Shifting gears consumes transmission fluidpressure. Consequently, the accumulator pressure is decreased.

Between time T12 and time T13, the transmission is downshifted severalmore times while RSS is active and the engine is stopped. Thetransmission gears are downshifted in response to the decreasing vehiclespeed so that if the driver increases the driver demand torque, thetransmission is in a gear suitable to transfer engine torque to thewheels without creating a driveline torque disturbance greater than athreshold torque. The transmission gears are partially engaged so thatthe transmission input shaft is not coupled to the transmission outputshaft. One of the plurality of clutches to engage each of theillustrated gears may be stroked or fully open. The transmissionelectric pump speed is increased in response to accumulator pressurereduction and shifting of the gears to partially activate gears. Theaccumulator pressure decreases several times and increases after initialdecrease due to the electric pump being activated.

At time T13, the RSS status transitions to a lower level. The RSS statusmay transition to a lower level in response to a driver releasing abrake pedal or applying an accelerator pedal. The engine is started andthe transmission's electric pump is stopped in response to engine speedexceeding a threshold speed where the mechanical pump supplies a desiredflow rate of transmission fluid. Further, 1^(st) gear is fully engagedby closing a plurality of clutches that engage 1^(st) gear. The vehiclealso begins to accelerate and the accumulator pressure is at a higherlevel.

Between time T13 and time T14, the transmission is upshifted throughmultiple transmission gears in response to increasing vehicle speed anddriver demand torque (not shown). The transmission's electric pumpremains deactivated and the accumulator pressure remains at a higherlevel.

At time T14, the RSS status transitions to a higher level. Consequently,the engine is stopped and the vehicle speed begins to decrease. Thevehicle speed decreases at a greater rate than between time T12 and timeT13. Therefore, the transmission skip downshifts from 5^(th) gear to3^(rd) gear and from 3^(rd) gear to 1^(st) gear. The electric pump speedis increased to a higher level in response to the short amount of timebetween shifts so that the electric pump may fill clutches quicker. Theaccumulator flow control valve is also opened (not shown) duringtransmission gear shifting. The transmission gears are partially engagedafter time T14 during the downshifting to 1^(st) gear. Consequently, theaccumulator pressure is reduced. The electric pump speed is reduced when1^(st) gear is entered to conserve electrical energy since furtherdownshifting is not possible. The engine remains stopped.

At time T15, the engine is restarted before vehicle speed is zero andthe RSS status transitions to a lower level. The engine is restarted inresponse to the RSS transitioning to a lower level. Shortly thereafter,the electric pump is deactivated in response to engine speed exceeding athreshold speed. First gear is fully engaged and the vehicle begins toaccelerate in response to an increased driver demand torque (not shown)that caused the RSS state change.

In this way, electric pump speed may be controlled to facilitatetransmission gear shifting when an engine is stopped. Further,transmission gears may be shifted while the engine is stopped to improvedriveline responsiveness and decrease the possibility of producingdriveline torque disturbances.

Referring now to FIG. 6, a method for operating a vehicle driveline isshown. The method of FIG. 6 may be incorporated into the system of FIGS.1-3 as executable instructions stored in non-transitory memory. Further,the method of FIG. 6 may provide the operating sequence as is shown inFIGS. 4 and 5. Further still, portions of the method of FIG. 6 may beactions taken by controller 12 in the physical world to transformvehicle operating states via one or more actuators or sensors.

At 602, method 600 determines vehicle conditions. Vehicle conditions mayinclude but are not limited to vehicle speed, engine speed, transmissionaccumulator pressure, driver demand torque, engaged or partially engagedtransmission gear, and ambient environmental conditions. Method 600proceeds to 604 after determining vehicle conditions.

At 604, method 600 judges whether or not rolling stop/start RSSconditions are met. RSS is a mode where an engine of the vehicle isstopped while the vehicle is rolling. However, in some examples, RSS mayalso include stopping the engine while the vehicle is stopped. RSS maybe activated in response to a driver demand torque that is less than athreshold. In one example, driver demand torque may be determined fromempirically determined values stored in a table or function. The tableor function is indexed based on accelerator pedal position and vehiclespeed. In other examples, RSS may be activated in response to otherconditions such as a brake pedal being activated and a low driver demandtorque. Thus, RSS may not be provided if the brake pedal is released. Ifmethod 600 judges that RSS conditions are met, the answer is yes andmethod 600 proceeds to 606. Otherwise, the answer is no and method 600proceeds to 620.

At 606, method 600 stops engine rotation by stopping fuel flow and sparkto the engine if the engine is not stopped. Further, method 600 shiftsthe transmission to neutral by opening one clutch of a plurality ofclutches that engage the presently engaged transmission gear. Theremaining clutches of the plurality of clutches that engage thepresently engaged transmission gear remain closed so that the presentlyengaged gear is partially engaged or activated. For example, if 5^(th)gear is activated by closing 1^(st), 3^(rd), and 6^(th) clutches, the3^(rd) clutch may be opened so that the transmission is in neutral and5^(th) gear is partially engaged. Note that the number of clutches toactivate a particular gear and the clutches that activate a particulargear may vary between different transmission types and are not intendedto limit this specification. The transmission electric pump may also beactivated by supplying electrical current to the electric pump. Thetransmission electric pump may not be activated if energy savings isprioritized over drivability at 608. If the transmission is alreadypartially engaging a gear, the gear remains partially engaged.

At 608, method 600 judges whether or not to prioritize vehicle energysavings over vehicle drivability. In one example, vehicle energy savingsmay have higher priority that vehicle drivability in response to adriver requesting improve vehicle energy savings via a switch orhuman/machine interface. If method 600 judges to prioritize vehicleenergy savings over vehicle drivability, the answer is yes and method600 returns to 604. In returning to 604, method 600 does not partiallyengage transmission gears to improve driveline response. If method 600judges not to prioritize vehicle energy savings over vehicledrivability, the answer is no and method 600 proceeds to 610. Thus, ifmethod 600 returns to 604, transmission clutches are not operated whenthe engine is stopped. Consequently, the time to reactivate the engineand supply torque to vehicle wheels may increase, but less energy may beconsumed by the vehicle.

At 610, method 600 estimates an amount of time between gear shifts. Inone example, method 600 determines the vehicle deceleration rate bysubtracting vehicle speed determined at a second time by vehicle speeddetermined at a first time and dividing the result by the differencebetween the second time and the first time. If the vehicle decelerationrate is less than a threshold, the transmission gears are sequentiallydownshifted one gear at a time (e.g., 5^(th) to 4^(th) to 3^(rd) to2^(nd) to 1^(st)). However, if the deceleration rate is greater than thethreshold, the transmission gears may be skip shifted (e.g., 5^(th) gearto 3^(rd) gear to 1^(st) gear). In one example, gear changes occuraccording to a shift schedule that is based on vehicle speed and driverdemand torque. Therefore, the amount of time between gear shifts may beestimated based on a speed that a gear is entered, a speed the gear isexited, and the vehicle deceleration rate. For example, if the vehicleis decelerating and 4^(th) gear is entered at 74 KPH and exited at 60KPH while the vehicle is decelerating at 2 KPH, the time between gearshifts is (74−60)/2=7 seconds. The transmission electric pump speed maybe adjusted in response to the time between shifts. Transmissionelectric pump speed may be increased by increasing current flow to thepump or decreased by decreasing current flow to the pump. For example,if the time between shifts is relatively short, the electric pump speedmay be higher to decrease clutch filling time. If the time betweenshifts is relatively long, the electric pump speed may be lower to fillthe clutch at a lower rate that reduces current supplied to the pump.Thus, if time between transmission gear shifts is increasing, electricpump speed may be decreased. If time between transmission gear shifts isdecreasing, electric pump speed may be increased to reduce clutchfilling time. Further, the transmission electric pump speed may beincreased as accumulator pressure decreases to reduce clutch fillingtime. At higher accumulator pressures, the electric pump speed may bereduced. Method 600 proceeds to 614 after electric pump speed isadjusted.

At 614, method 600 maintains the transmission in neutral with apartially engaged gear. Further, method 600 shifts transmission gears topartially engage transmission gears based on a gear shift schedule. Thegear that is partially engaged is based on vehicle speed and driverdemand torque, which are used to index the gear shift schedule ofpredetermined gear values. Method 600 may engage and release a pluralityof clutches via clutch pressure control valves while partially engagingselected gears. For example, method 600 may stroke clutch number one(e.g., supply fluid to clutch number one such that the torque transfercapacity of clutch number one is less than a threshold) and fully closeclutches numbered two and five to partially engage 4^(th) gear. Thetransmission may be downshifted from 4^(th) gear to partially engage3^(rd) gear by opening clutch number five and closing clutch numberthree while clutch number two remains fully closed and clutch number oneis stroked. The transmission remains in neutral during the shifting ofgears to partially engage the scheduled gears. Method 600 returns to 604after shifting transmission gears.

Additionally, the accumulator flow control valve may be commanded openeach time a clutch is commanded closed and the accumulator flow controlvalve may be closed once the commanded clutches are closed.

At 620, activates the engine by engaging a starter and supplying sparkand fuel to the engine if the engine is not already started. Method 600proceeds to 622 after engine starting is initiated.

At 622, method 600 judges if the transmission is engaged in a gear. Ifso, the answer is yes and method 600 proceeds to 632. Otherwise, theanswer is no and method 600 proceeds to 624.

At 624, method 600 engages a transmission gear. If a transmission gearis not partially engaged all transmission clutches to activate aparticular gear based on the transmission gear shift schedule are closedby adjusting the clutch pressure control valves. If the transmissiongear to be engaged is partially engaged, the stroked clutch is fullyclosed to engage the gear. The engaged gear is based on output of thetransmission gear shift schedule. The accumulator flow control valve maybe commanded open in response to a request to close one or moreclutches. The accumulator flow control valve may be commanded closed inresponse to the one or more clutches being closed.

In addition, if the transmission electric pump is not activated, it maybe activated at 624 to begin closing the clutches while engine speed istoo low to provide a desired amount of flow through the mechanicaltransmission pump. Method 600 also adjusts the transmission electricpump speed in response to accumulator pressure. Method 600 proceeds to626 after the clutches are commanded to engage the gear output from theshift schedule.

At 626, method 600 judges if engine speed is greater than a thresholdspeed. In one example, the threshold speed is a speed at which themechanically driven transmission pump outputs a desired flow rate oftransmission fluid. If method 600 judges that engine speed is notgreater than the threshold speed, the answer is no and method 600returns to 624. Otherwise, the answer is yes and method 600 proceeds to628.

At 628, method 600 deactivates the transmission electric pump. Theelectric pump is deactivated by ceasing current flow to the electricpump. Method 600 proceeds to 630 after the transmission electric pump isdeactivated.

At 630, method 600 fully engages the selected gear output from thetransmission shift schedule via controlling clutch pressure as shown inFIG. 4. The clutches are supplied fluid via the clutch pressure controlvalves and the mechanically driven pump. Method 600 proceeds to 632after fully closing the clutches.

At 632, the transmission clutches are controlled via clutch pressurecontrol valves and transmission gears are selected and engaged based ona transmission shift schedule. Method 600 proceeds to exit afterclutches and gears are operated according to a transmission gear shiftschedule.

In this way, the method of FIG. 6 provides for adjusting speed of atransmission electric pump to reduce electrical consumption and timelyclose selected clutches that engage a gear output from a transmissionshift schedule that is stored in controller memory. Further, the methodof FIG. 6 adjusts electric pump speed by adjusting current supplied tothe electric pump based on an amount of time between gear shifts.

Thus, the method of FIG. 6 provides for a method for operating a vehicledriveline, comprising: activating an electric transmission pump inresponse to a request to stop an engine; and adjusting a speed of theelectric transmission pump in response to a pressure in an accumulator.The method includes where the accumulator is positioned downstream ofthe electric transmission pump and downstream of a mechanically driventransmission pump. The method further comprises opening a valve at anoutlet side of the accumulator in response to a request to stroke a gearclutch.

In some examples, the method further comprises starting the engine inresponse to an increase in driver demand torque or release of a brakepedal and closing the valve after the valve is open during a most recentengine start in response to engine speed exceeding a threshold speedafter starting the engine. The method further comprises opening thevalve in response to the pressure in the accumulator being less than athreshold pressure and a gear of a transmission being fully engagedafter a first time the valve is closed after the most recent enginestart. In this way, the clutch may be filled faster and then theaccumulator may be recharged to a higher pressure without increasing thetime to fill and close the clutch. The method further comprises startingthe engine in response to an increase in driver demand torque or releaseof a brake pedal and deactivating the electric transmission pump inresponse to engine speed exceeding a threshold speed after starting theengine. The method further comprises partially engaging a gear of atransmission by fully engaging one or more transmission clutches andstroking a transmission clutch without fully closing the transmissionclutch.

The method of FIG. 6 also provides for a method for operating a vehicledriveline, comprising: activating an electric transmission pump inresponse to a request to stop an engine; and adjusting a speed of theelectric transmission pump in response to an estimate of an amount oftime between transmission gear shifts. The method includes where theamount of time is based on a vehicle deceleration rate and a gear shiftschedule. The method further comprises adjusting the speed of theelectric transmission pump in response to a pressure in an accumulatorpositioned downstream of the electric transmission pump. The methodfurther comprises starting the engine after stopping the engine anddeactivating the electric transmission pump in response to engine speedexceeding a threshold speed a first time after a most recent enginestart.

In some examples, the method further comprises an accumulator positioneddownstream of the electric transmission pump and a mechanicaltransmission pump, and opening a valve on an outlet side of theaccumulator in response to a request to stroke a transmission gearclutch. The method further comprises partially activating a plurality oftransmission gears by fully closing one or more clutches for each of theplurality of transmission gears and stroking, but not fully closing, oneclutch for each of the plurality of transmission gears while the enginehas stopped rotating. The input speed of the one clutch that is notfully closed (e.g., the stroked clutch) is not equal to an output speedof the stroked clutch. The method further comprises opening and closinga valve located at an outlet side of an accumulator each time the oneclutch for each of the plurality of transmission gears that is not fullyclosed is stroked to partially activate one of the plurality oftransmission gears. In this way, pressure in the accumulator may beconserved.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware to manipulateoperating states of the various devices disclosed. As will beappreciated by one of ordinary skill in the art, the methods describedin FIG. 6 may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various steps or functionsillustrated may be performed in the sequence illustrated, in parallel,or in some cases omitted. Likewise, the order of processing is notnecessarily required to achieve the objects, features, and advantagesdescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated steps orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, the methods described herein may be acombination of actions taken by a controller in the physical world andinstructions within the controller.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 enginesoperating in natural gas, gasoline, diesel, or alternative fuelconfigurations could use the present description to advantage.

1-7. (canceled)
 8. A method for operating a vehicle driveline,comprising: activating an electric transmission pump in response to arequest to stop an engine; and adjusting a speed of the electrictransmission pump in response to an estimate of an amount of timebetween transmission gear shifts.
 9. The method of claim 8, where theamount of time is based on a vehicle deceleration rate and a gear shiftschedule.
 10. The method of claim 8, further comprising adjusting thespeed of the electric transmission pump in response to a pressure in anaccumulator positioned downstream of the electric transmission pump. 11.The method of claim 8, further comprising starting the engine afterstopping the engine and deactivating the electric transmission pump inresponse to engine speed exceeding a threshold speed a first time aftera most recent engine start.
 12. The method of claim 8, furthercomprising an accumulator positioned downstream of the electrictransmission pump and a mechanical transmission pump, and opening avalve on an outlet side of the accumulator in response to a request tostroke a transmission gear clutch.
 13. The method of claim 8, furthercomprising partially activating a plurality of transmission gears byfully closing one or more clutches for each of the plurality oftransmission gears and stroking, but not fully closing, one clutch foreach of the plurality of transmission gears while the engine has stoppedrotating.
 14. The method of claim 13, further comprising opening andclosing a valve located at an outlet side of an accumulator each timethe one clutch for each of the plurality of transmission gears that isnot fully closed is stroked to partially activate one of the pluralityof transmission gears.
 15. A vehicle system, comprising: an engine; atransmission coupled to the engine and including a torque converterhaving a torque converter clutch, an electric pump, a mechanical pump,an accumulator positioned downstream of the electric pump and themechanical pump, and a valve positioned at an outlet side of theaccumulator; a controller including executable instructions stored in anon-transitory memory for selectively stroking a transmission gearclutch without fully closing the transmission gear clutch in response toa request to improve vehicle drivability at expense of vehicle energyconsumption, and to not stroke the transmission gear clutch in responseto a request to improve vehicle energy consumption at expense of vehicledrivability, the transmission clutch stroked or not stroked while theengine is stopped.
 16. The vehicle system of claim 15, furthercomprising additional instructions for adjusting a speed of the electricpump in response to an estimate of an amount of time betweentransmission gear shifts.
 17. The vehicle system of claim 15, furthercomprising additional instructions for adjusting a speed of the electricpump in response to a pressure in the accumulator.
 18. The vehiclesystem of claim 15, further comprising additional instructions forstopping rotation of the engine in response to a driver demand torque.19. The vehicle system of claim 18, further comprising additionalinstructions to shift the transmission to neutral in response to thedriver demand torque.
 20. The vehicle system of claim 19, furthercomprising additional instructions to activate the electric pump inresponse to the driver demand torque.